This invention relates to an apparatus for the on-site generation of polyurethane foam. More particularly, this invention relates to an apparatus of this type having improved means for automatically cleaning the mixing chamber thereof.
Several portable apparatus have been disclosed in the art for the generation of polyurethane foam. See, for example, U.S. Pat. No. 3,178,157, issued to Cole on Apr. 3, 1965; U.S. Pat. No. 3,541,023, which issued Nov. 17, 1970 to Cole; and U.S. Pat. No. 3,769,232, which issued Oct. 30, 1973, to Houldridge. Apparatus of this type usually includes two storage tanks for supplying two inter-reactive polyurethane-foaming materials, means for imposing a gas pressure in these tanks to expell the reactants therefrom and a mixing chamber having an outlet and two valved inlets for mixing the reactants before they are dispersed as a foaming mixture from the mixing chamber. These prior art apparatus permit dispersing of polyurethane foam on-site for use in an increasing number of applications, such as making molded foam insulation, furniture parts, structural elements, packaging, and so forth.
It has been found desirable to periodically flush the mixing chamber wth a suitable solvent to clean the mixing chamber and remove any material which has accumulated therein. Build-up of material could result in improper mixing, poor flow characteristics, and improper ratio of ingredients, all of which could effect the quality of foam produced.
For the purpose of cleaning the mixing chamber, the apparatus may include a solvent tank which is connected to the mixing chamber to provide a supply of solvent for flushing purposes. Such arrangement is shown, for example, in previously mentioned U.S. Pat. Nos. 3,769,232 and 3,541,023.
During the flushing operation of previously known apparatus, solvent is expelled onto the floor or ground or into a separate container. This results in a waste of solvent and increased expense. In addition, if the solvent is expelled directly onto the floor or ground, it presents an ecological problem as the solvent constitutes a pollutant.
In the above-mentioned copending application Ser. No. 656,157, there is disclosed an improvement in an on-site foam generating apparatus wherein means for recovering the cleaning solvent within the apparatus is provided, with the solvent being recycled through the mixing chamber when an appropriate valve is activated. The present invention is an improvement on the apparatus disclosed in that application and provides an automatic solvent recycling system. In addition, an automatic gas purge system may be provided.
According to the invention, the apparatus is of the type wherein two inter-reactive foam-forming materials are mixed and foam generated. The apparatus includes a foam gun head having a mixing chamber for mixing the materials. Solvent storage means are provided for storing a solvent. The improvement comprises, in general terms, means for supplying solvent from the solvent storage tank to said mixing chamber through an electrically activated solvent valve when said valve is in a first position and for by-passing the mixing chamber and returning the solvent directly to the solvent storage means when the solvent valve is in a second position. Electrical sensing means are provided for sensing the presence of the foam gun head in a first position wherein said foam gun head is in a position to discharge solvent from the mixing chamber into the solvent storage tank. Electrical circuit means is responsive to the electrical sensing means sensing the presence of the foam gun head in the first position to actuate the solvent valve means to move it to its first position and responsive to the removal of said foam gun head from the first position to move said solvent valve to its second position.
In addition, means for supplying purging gas to the mixing chamber may be provided through an electrically actuated purging gas valve which is normally closed. An electrical circuit in response to the electrical sensing means senses the removal of the foam gun head from its first position and causes the opening of the purging gas valve for a predetermined time period to provide a blast of purging gas through the mixing chamber.